As is known, power conversion from a laser carrier frequency to the desired sideband frequency in the cases of double sideband and baseband modulators is severely limited by the fact that the modulated output power spectrum is distributed into two infinite series of upper and lower sideband signals. Consequently, the maximum power converted into the lowest order sideband can only reach about twenty percent of the total input power. Beyond this level, a large fraction of the power provided to a device generates high-order sideband signals. It has been demonstrated as early as 1962 at a HeNe laser wavelength and later in 1979 at the 10.6 microns CO.sub.2 laser wavelength that it is possible to generate only a single sideband within a select frequency range at nearly 100 percent conversion efficiency. This is accomplished by creating either a right-hand or left-hand rotating optical indicatrix at an angular velocity .omega..sub.m /2, where .omega..sub.m is the frequency of either a left-hand or a right-hand circularly polarized microwave which is launched into an electro-optic crystal having the proper orientation. If a circularly polarized optical wave is also launched into the crystal with the same sense of rotation to that of the microwave, the modulated output power spectrum would consist of the carrier and only one circularly polarized sideband at a frequency .omega..sub.m offset from the carrier frequency .omega..sub.o with an opposite sense of rotation, provided that a perfect phase-velocity match exists between the two travelling waves. However, the drive power required to generate 90 percent power conversion at the 10 micron laser wavelength can be as high as 60 kW using a bulk electro-optic crystal. It would be advantageous to have a single sideband microwave modulator characterized by high conversion efficiency and reduced microwave driving power. The present invention is drawn towards such a device.